Group II-I-V materials such as the GaN material system are particularly useful in constructing lasers and LEDs in the blue and green wavelengths. The construction of an optical device based on these materials typically begins with the deposition of a layer III-V material on a substrate such as sapphire or Si. Ideally, one would like to grow an optical device such as a laser on silicon so that additional circuit components can be fabricated on the same die. Because of the lattice mismatch, such growth is not currently practical. Accordingly, lasers are often grown on sapphire. However, there is still a significant mismatch in the lattice constants of sapphire and GaN. For example, the lattice constant for GaN differs from that of sapphire by approximately 13-16%. During the growth of the GaN layer, the substrate and the GaN layer tend to keep their original lattice parameters; hence, there is a mismatch between the lattice parameters between the two layers. This mismatch generates stress in the GaN layer which, in turn, leads to defects in the layer. Such defects interfere with the construction of further layers on the base layer and reduce the yield of usefull devices.
Broadly, it is the object of the present invention to provide an improved method for growing Group III-V layers on a substrate having a substantially different lattice constant.
It is a further object of the present invention to provide a method for growing GaN on Si in which the stress generated by the lattice mismatch is substantially reduced.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.